DESCRIPTION

Network protocols installed in the system are maintained within what are
called domains (for example the inetdomain and localdomain).
struct domain {
int dom_family; /* AF_xxx */
char *dom_name;
void (*dom_init) /* initialize domain data structures */
(void);
int (*dom_externalize) /* externalize access rights */
(struct mbuf *, struct mbuf **);
void (*dom_dispose) /* dispose of internalized rights */
(struct mbuf *);
struct protosw *dom_protosw, *dom_protoswNPROTOSW;
struct domain *dom_next;
int (*dom_rtattach) /* initialize routing table */
(void **, int);
int dom_rtoffset; /* an arg to rtattach, in bits */
int dom_maxrtkey; /* for routing layer */
};
Each domain contains an array of protocol switch structures (structprotosw*), one for each socket type supported.
struct protosw {
short pr_type; /* socket type used for */
struct domain *pr_domain; /* domain protocol a member of */
short pr_protocol; /* protocol number */
short pr_flags; /* see below */
/* protocol-protocol hooks */
pr_input_t *pr_input; /* input to protocol (from below) */
pr_output_t *pr_output; /* output to protocol (from above) */
pr_ctlinput_t *pr_ctlinput; /* control input (from below) */
pr_ctloutput_t *pr_ctloutput; /* control output (from above) */
/* utility hooks */
pr_init_t *pr_init;
pr_fasttimo_t *pr_fasttimo; /* fast timeout (200ms) */
pr_slowtimo_t *pr_slowtimo; /* slow timeout (500ms) */
pr_drain_t *pr_drain; /* flush any excess space possible */
struct pr_usrreqs *pr_usrreqs; /* supersedes pr_usrreq() */
};
The following functions handle the registration of a new domain, lookups
of specific protocols and protocol types within those domains, and handle
control messages from the system.
pfctlinput() is called by the system whenever an event occurs that could
affect every domain. Examples of those types of events are routing table
changes, interface shutdowns or certain ICMP message types. When called,
pfctlinput() calls the protocol specific pr_ctlinput() function for each
protocol in that has defined one, in every domain.
pfctlinput2() provides that same functionality of pfctlinput(), but with
a few additional checks and a new void* argument that is passed directly
to the protocol’s pr_ctlinput() function. Unlike pfctlinput(),
pfctlinput2() verifies that sa is not NULL, and that only the protocol
families that are the same as sa have their pr_ctlinput() function
called.
net_add_domain() adds a new protocol domain to the system. The argument
data is cast directly to structdomain* within the function, but is
declared void* in order to prevent compiler warnings when new domains
are registered with SYSINIT(). In most cases net_add_domain() is not
called directly, instead DOMAIN_SET() is used.
If the new domain has defined an initialization routine, it is called by
net_add_domain(); as well, each of the protocols within the domain that
have defined an initialization routine will have theirs called.
Once a domain is added it cannot be unloaded. This is because there is
no reference counting system in place to determine if there are any
active references from sockets within that domain.
pffindtype() and pffindproto() look up a protocol by its number or by its
type. In most cases, if the protocol or type cannot be found, NULL is
returned, but pffindproto() may return the default if the requested type
is SOCK_RAW, a protocol switch type of SOCK_RAW is found, and the domain
has a default raw protocol.
Both functions are called by socreate() in order to resolve the protocol
for the socket currently being created.
DOMAIN_SET() is a macro that simplifies the registration of a domain via
SYSINIT(). The code resulting from the macro expects there to be a
domain structure named “namedomain” where name is the argument to
DOMAIN_SET():
struct domain localdomain =
{ AF_LOCAL, "local", unp_init, unp_externalize, unp_dispose,
localsw, &localsw[sizeof(localsw)/sizeof(localsw[0])] };
DOMAIN_SET(local);

RETURNVALUES

Both pffindtype() and pffindproto() return a structprotosw* for the
protocol requested. If the protocol or socket type is not found, NULL is
returned. In the case of pffindproto(), the default protocol may be
returned for SOCK_RAW types if the domain has a default raw protocol.